In the manufacture of two piece cans, a punch on a bodymaker ram is used to push a drawn metal cup through wall ironing dies in order to iron the side wall and make a taller can. After passing through dies, the punch carries the drawn and wall ironed can into contact with a doming station.
Although the ram is supported in bearings, alignment of the ram will vary due to friction and wear. In addition, vibration of a high speed reciprocating ram means that the can still does not always contact the doming station in a fully concentric and aligned position.
Undesirable vibration of the ram will arise not only due to the variable ‘droop’ of the cantilever supported ram as it moves towards and back from its fully extended position, but also due to the impact of the can at the dome forming station.
Misalignment of the ram/punch when it carries a can into contact with the doming station will ultimately lead to split domes, particularly in aluminium cans. When the ram is only slightly misaligned, an arcuate split (referred to hereinafter as a ‘smile’) in the base of the can could arise which subsequently may result in burst cans at the fillers or customer. Base faults like smiles are not easily detectable by the naked eye during manufacture.
This invention seeks to provide an apparatus for detecting base defects such as split domes during manufacture and for measuring ram alignment dynamically.